问如何在鼠标悬停在数据点上时显示工具提示

EN

  private void DefineSeries() {
     var series = new Series();
     series.ToolTip = "#VALY";
     series.PostBackValue = "#Index";
     var x = new[] {0, 1, 2, 3, 4, 5};
     var y = new[] {0, 4, 5, 3, 7, 2};
     for ( int i = 0; i < x.Length; i++ ) {
         series.Points.Add( new DataPoint( x[ i ], y[ i ] ) );
     }
     series.ChartType = SeriesChartType.Line;
     DefineSeriesStyle( series );
     chart_.Series.Add( series );   
  }

  public ActionResult CausedOutPoint() {
     var causedOut = new CausedOutViewModel();
     var path = Server.MapPath( "~" ) + "CausedOut.Png";
     causedOut.Chart.SaveImage( path, ChartImageFormat.Png );
     return File( path, "img/png" );
  }

  public CausedOutViewModel() {
     chart_ = new Chart {IsMapEnabled = true};
     chart_.PostPaint += chart__PostPaint;
     chart_.RenderType = RenderType.ImageMap;
     chart_.ID = "CausedOut";
     InitializeChart( chart_ );
     chart_.Width = new Unit( 1200, UnitType.Pixel );
     chart_.Height = new Unit( 800, UnitType.Pixel );
     CreateTitles();
  }

  private void InitializeChart( ) {
     DefineSeries();
     DefineChartArea();
  }